(1) Field of the Invention
This invention relates to an improved electrically-conductive polyolefin resin composition which can receive direct electroplating to exhibit excellent plate adhesion properties.
(2) Description of the Prior Art
Conventionally, a number of polyolefin resin compositions capable of direct electroplating are well known. One example of such resin compositions is disclosed in Japanese Patent Liad-Open No. 60349/'79. This resin composition comprises, in addition to a polyolefin resin, 25-41% of an electrically-conductive carbon black, 0.15-1.5% of sulfur, 0-7% of zinc oxide, and 0.2-1.5% of mercaptobenzothiazole or mercaptobenzothiazyl disulfide, and is commercially available from Alloy Polymers Co., Inc. under the trade name of Caprez DPP. Another resin composition, which is disclosed in Japanese Patent Laid-Open Nos. 58235/'80, 58236/'80, and 58237/'80, comprises a polyolefin resin, an oxide of a metal of group II in the periodic table, sulfur, a vulcanization accelerator, and an electrically-conductive carbon black. However, these resin compositions exhibit such poor flow properties during molding that small-sized articles cannot be made by multiple molding, a large gate is required for the molding of medium-sized articles, and large-sized thin-wall articles suitable for practical use cannot be molded because of the ensuing poor surface conditions. Thus, the electrically-conductive resin compositions known in the prior art have the disadvantage that their freedom of product design is significantly restricted by consideration of their resin flow properties.
On the other hand, it is well known that softening agents derived from petroleum and polyalkylene glycols (such as polyethylene glycol and the like) are being used as flow improvers in some fields of the rubber and resin industry. However, it has been believed in the polyolefin resin art that, if such a flow improver is added to a resin composition for use as in substrates to be plated, the flow improver will bleed on the surface of the molded articles made thereof and thus impair the adhesion properties of the plate formed thereon.
Prior to this invention, the present inventors found that specific thiuram disulfide compounds are effective plate adhesion promoters for olefin polymers containing carbon black and sulfur, and provided resin compositions containing such compounds. In addition, the present inventors have now found that the addition of a flow improver to these resin composiions can significantly improve their molding flow properties without impairing the plate adhesion properties, and that the flow improver remains effective even when a wide variety of other plate adhesion promoters are used. The present invention has been completed on the basis of this discovery.